850 research outputs found
Absence of zero-temperature transmission rate of a double-chain tight-binding model for DNA with random sequence of nucleotides in thermodynamic limit
The zero-temperature transmission rate spectrum of a double-chain
tight-binding model for real DNA is calculated. It is shown that a band of
extended-like states exists only for finite chain length with strong
inter-chain coupling. While the whole spectrum tends to zero in thermodynamic
limit, regardless of the strength of inter-chain coupling. It is also shown
that a more faithful model for real DNA with periodic sugar-phosphate chains in
backbone structures can be mapped into the above simple double-chain
tight-binding model. Combined with above results, the transmission rate of real
DNA with long random sequence of nucleotides is expected to be poor.Comment: 5 pages, 9 figure
Diffusion limited aggregation as a Markovian process. Part I: bond-sticking conditions
Cylindrical lattice Diffusion Limited Aggregation (DLA), with a narrow width
N, is solved using a Markovian matrix method. This matrix contains the
probabilities that the front moves from one configuration to another at each
growth step, calculated exactly by solving the Laplace equation and using the
proper normalization. The method is applied for a series of approximations,
which include only a finite number of rows near the front. The matrix is then
used to find the weights of the steady state growing configurations and the
rate of approaching this steady state stage. The former are then used to find
the average upward growth probability, the average steady-state density and the
fractal dimensionality of the aggregate, which is extrapolated to a value near
1.64.Comment: 24 pages, 20 figure
The theory of magnetic field induced domain-wall propagation in magnetic nanowires
A global picture of magnetic domain wall (DW) propagation in a nanowire
driven by a magnetic field is obtained: A static DW cannot exist in a
homogeneous magnetic nanowire when an external magnetic field is applied. Thus,
a DW must vary with time under a static magnetic field. A moving DW must
dissipate energy due to the Gilbert damping. As a result, the wire has to
release its Zeeman energy through the DW propagation along the field direction.
The DW propagation speed is proportional to the energy dissipation rate that is
determined by the DW structure. An oscillatory DW motion, either the precession
around the wire axis or the breath of DW width, should lead to the speed
oscillation.Comment: 4 pages, 2 figure
Fatigue Damage Analysis of an Asphalt Mixture Based on Pseudostiffness
The fatigue damage characteristics of an asphalt mixture were analyzed, a new fatigue damage model was constructed based on the Schapery pseudovariable theory and continuum damage mechanics. According to the Schapery theory and the generalized elastic-viscoelastic correspondence principle, the experimental stress–strain curves of the asphalt mixture are transformed into the stress vs. pseudostrain curves. The relation between stress and pseudostrain is shown to be linear, which eliminates the viscoelastic hysteresis effect of the asphalt mixture and its time dependence.Выполнен анализ характеристик усталостного повреждения битумной смеси. Построена новая модель усталостного повреждения на основании псевдопараметрической теории Шапери и механики повреждения сплошных сред. В соответствии с теорией Шапери и обобщенным принципом соответствия между упругими и вязкоупругими деформациями экспериментальные кривые напряжение–деформация для битумной смеси преобразуются в кривые напряжение–псевдодеформация. Показано, что последняя линейна, что устраняет вязкоупругий эффект гистерезиса битумной смеси и его временную зависимость
Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices
We examine how the current--voltage characteristics of a doped weakly coupled
superlattice depends on temperature. The drift velocity of a discrete drift
model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated
as a function of temperature. Numerical simulations and theoretical arguments
show that increasing temperature favors the appearance of current
self-oscillations at the expense of static electric field domain formation. Our
findings agree with available experimental evidence.Comment: 7 pages, 5 figure
Comparison of Structural Development and Biochemical Accumulation of Waxy and Non-waxy Wheat Caryopses
This study was conducted to compare structural development and biochemical accumulation of waxy and non-waxy wheat (NW) caryopses. The caryopses’ microstructure of the waxy wheat (WW) and NW cultivars at different developmental stages were observed under light, fluorescence, and scanning electron microscope. The results were as follows: Compared with NW,WWhad a shorter maturation duration, which was reflected in several following characteristics. Programmed cell death of the pericarp began earlier, and the chlorophyll-containing layer in the pericarp was smaller. Vacuoles in chalazal cells accumulated more tannins at different developmental stages. Starch granules and protein bodies in the endosperm showed a higher accumulation level in developing caryopses, and aleurone cells were larger in size with larger numbers of aleurone grains. An analysis of the element content indicated that the mineral elements Mg, P, K, and Ca exhibited a higher content, while the heavy elements Cr, Cd, and Pb exhibited a lower content in the aleurone layer
STM characterization of the Si-P heterodimer
We use scanning tunneling microscopy (STM) and Auger electron spectroscopy to
study the behavior of adsorbed phosphine (PH) on Si(001), as a function
of annealing temperature, paying particular attention to the formation of the
Si-P heterodimer. Dosing the Si(001) surface with 0.002 Langmuirs of
PH results in the adsorption of PH (x=2,3) onto the surface and
some etching of Si to form individual Si ad-dimers. Annealing to 350C
results in the incorporation of P into the surface layer to form Si-P
heterodimers and the formation of short 1-dimensional Si dimer chains and
monohydrides. In filled state STM images, isolated Si-P heterodimers appear as
zig-zag features on the surface due to the static dimer buckling induced by the
heterodimer. In the presence of a moderate coverage of monohydrides this static
buckling is lifted, rending the Si-P heterodimers invisible in filled state
images. However, we find that we can image the heterodimer at all H coverages
using empty state imaging. The ability to identify single P atoms incorporated
into Si(001) will be invaluable in the development of nanoscale electronic
devices based on controlled atomic-scale doping of Si.Comment: 6 pages, 4 figures (only 72dpi
Analysing Lyapunov spectra of chaotic dynamical systems
It is shown that the asymptotic spectra of finite-time Lyapunov exponents of
a variety of fully chaotic dynamical systems can be understood in terms of a
statistical analysis. Using random matrix theory we derive numerical and in
particular analytical results which provide insights into the overall behaviour
of the Lyapunov exponents particularly for strange attractors. The
corresponding distributions for the unstable periodic orbits are investigated
for comparison.Comment: 4 pages, 4 figure
Comparison of endosperm amyloplast development and degradation in waxy and non-waxy wheat
The waxy wheat shows special starch quality due to high amylopectin content. However, little information is available concerning the development and degradation of amyloplast from waxy wheat endosperm. To address this problem, waxy wheat variety, Yangnuo 1, and a non-waxy wheat variety, Yangmai 13, were chosen to investigate the development and degradation of endosperm amyloplast during wheat caryopsis development and germination stage respectively using histochemical staining and light microscopy. Changes of morphology, the soluble sugar and total starch content were indistinguishable in the process of caryopsis development of two wheat varieties. The developing endosperm of non-waxy was stained blue-black by I2-KI while the endosperm of waxy wheat was stained reddish-brown, but the pericarp of waxy and non-waxy wheat was stained blue-black. In contrast to nonwaxy wheat, endosperm amyloplast of waxy wheat had better development status and higher proportion of small amyloplast. During seed germination many small dissolution pores appeared on the surface of endosperm amyloplast and the pores became bigger and deeper until amyloplast disintegrated. The rate of degradation of waxy wheat endosperm amyloplast was faster than non-waxy wheat. Our results may also be helpful to the use of waxy starch in food and nonfood industry
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